FIG. 1 depicts a schematic diagram of local telecommunication network 100 in the prior art, in which the network provides telecommunication service to a number of subscribers that are situated within a geographic region. The core of local telecommunication network 100 is central office 101, which comprises at least one switch. The switch or switches at central office 101 connect subscribers in a given area to the public switched telephone network. The public switched telephone network is not actually part of any local network, but is a collection of switches and specific paths called “trunks” that connect the switches. Typically, the switch at central office 101 is connected to the rest of local telecommunication network 100 through a main distributing frame (abbreviated MDF) to large-capacity cable forming the first transmission facility, commonly referred to as F1 cable, at the exchange end of what is known as the local loop.
Typically, F1 cable 111 contains 1200 cable pairs. The wire pairs, or line pairs, are made of copper and are twisted to minimize crosstalk. F1 cable 111 is connected to cross-connect 103-1. As defined in Newton's Telecom Dictionary, 17th Edition, a “cross-connect” is defined as a connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers that attach to connecting hardware on each end. At cross-connect 103-1, those 1200 pairs are separated into smaller units, with two cables containing 500 pairs each, represented by cable 112 and 113, and two other cables containing 100 pairs each, represented by cable 114 and 115. F2 cable 115 is connected to cross-connect 103-2. At cross-connect 103-2, those 100 pairs are separated into smaller units, with one cable containing 75 pairs, represented by cable 116, and one other cable containing 25 pairs, represented by cable 117. The final run, F3 cable 117, is connected to cross-connect 103-3. In other local networks, possibly different numbers of cross-connects and cables are used. It is common for facilities numbering as high as F8 to be used, even though illustrative local telecommunication network 100 uses only F1 through F3.
Also constituting local telecommunication network 100 are telephone 104-1 through 104-25, served by line pairs connected to cross-connect 103-3. A cross-connect, such as cross-connect 103-3, that is used to split out line pairs for individual telephones is also referred to as a drop service terminal or, simply, a service terminal. The telephone terminals are at the subscriber end of the local loop. A specific loop path spanning local telecommunication network 100 serves each subscriber.
Note that cable 112, 113, 114, and 116 are connected to other cross-connects not shown in FIG. 1. It is possible that each active line pair within each of cable 112, 113, 114, and 116 terminates eventually at a telephone terminal at the subscriber end of the particular local loop served by the cable.
The segment of a local loop between the central office and the first outside plant node, that node being represented in FIG. 1 by cross-connect 103-1, can comprise a physical pair of wires or can comprise a virtual feeder pair in the form of a digital loop carrier (DLC) time slot. Similarly, just as F1 cable 111 can use virtual pairs, subsequent distribution legs (i.e., F2 cable 115 and F3 cable 117) can, use virtual pairs as well. The segments of local loop extending beyond cross-connect 103-1 are generally called distribution pairs. The last segment of local loop before each of telephone 104-1 through 104-25 is called a drop pair, or simply a drop.
Differing terms are sometimes used to describe cross-connects, such as feeder-distribution interface (FDI), remote terminal, and serving terminal, depending on where the cross-connect is situated in the local loop and the format of the signal the cross-connect handles. In all cases, cross-connects are the same in that they are demarcation points at which one transmission segment ends and another begins. Furthermore, at a most fundamental, conceptual level, cross-connects are the same. Such a logical extension of concepts should also be extended to varying arrangements in which the virtual feeder or distribution (for example, in the form of a digital loop carrier or a fiber) may be used not only for the F1 cable, but for any facility or leg of a subscriber loop.
An efficient process of maintenance for local loops depends on the ability to test subscriber lines at any time without dispatching technicians. Typically the biggest source of expense is the labor cost associated with dispatching into the field to manually make cross-connections in the FDIs and remote and serving terminals. Worse yet, the work typically performed for a new line or maintenance change in the local loop plant requires line rearrangements. For a significant number of those rearrangements, errors will almost inevitably occur, either in the rearrangement itself or in one or more administrative database entries made due to those changes. Error creation introduces even more expense to correct the errors.
Regardless of the subscriber service, the ability to test at the time a customer calls to report a trouble or at any time is crucial for efficient maintenance. These tests must be performed quickly and ideally without dispatching a field technician. Speed is important so that at least some common problems can be diagnosed (and ideally repaired) while the subscriber is on the phone with a repair service agent. For example, a common problem occurs when a subscriber leaves his phone off-hook. This can occur when a subscriber with two phones connected to one line leaves one phone off-hook during a conversation to pick up his other phone and forgets to hang up the phone used originally. After some time of sounding the receiver off-hook signal, the serving central office times out and essentially disconnects the subscriber's line. When the subscriber later tries to make a call using the second phone that was properly hung up, unaware that the first line is still off-hook, the phone line is perceived as broken. This subscriber might then call customer service complaining that he is unable make a call. Test equipment currently in common use (e.g., the Mechanized Loop Test, or MLT, provided by Lucent Technologies to Bell operating companies, etc.) can detect the receiver-off-hook condition and the repair agent can remind the subscriber to check his other phone lines, knowing that receiver-off-hook is likely the problem. On such a call, no technician is dispatched; indeed, even the process of recording this trouble call can be skipped, although it is likely recorded for statistical purposes. As the preceding description shows, this trouble call is efficiently handled because test equipment, which is sophisticated enough to detect the receiver-off-hook condition, can be switched onto any subscriber's line quickly and run tests while the subscriber is talking with a customer service agent. Such efficiency is vital to modern telephone system operations; service would no longer be affordable if such capabilities were unavailable.
Issues such as the one described above concern both testing (particularly centralized testing) and maintenance, as these two activities are inextricably intertwined within many telephone company operations.
Often, the problem the subscriber is having with her phone service is not as straightforward as, for example, a phone line being off-hook. There is occasionally something wrong with the local loop between the central office and the subscriber's telephone. While there are some repairs that can be effected remotely, usually the technician has to diagnose the problem, determine where along the line the problem is, and repair the problem (e.g., a physical break in the line, etc.). If the problem turns out to be a broken line, the technician can mend the actual break in the wire or can reconfigure the local loop so that the subscriber is assigned a new physical line. Ideally, only the specific segment between cross-connects or splices to where the problem has been localized is swapped out.
One issue with swapping out a line, for testing or re-provisioning purposes, is that the technician has to visit at least two places along the local loop for the subscriber. One place is the cross-connect or splice on the exchange side of the impairment, and the other place is the cross-connect or splice on the subscriber side of the impairment. The technician typically has to access a manual cross-connect box, depicted in FIG. 2 of the prior art. This box typically comprises mechanical connecting terminals called punchdown blocks. Line pairs on the exchange side are mechanically connected to one set of punchdown blocks, whereas line pairs on the subscriber side are mechanically connected to a second set of punchdown blocks. Each exchange-side line pair is then connected to the corresponding subscriber-side line pair by a jumper wire pair running from one punchdown block to the other. There is a plurality of exchange-side line pairs and a plurality of subscriber-side line pairs terminating at the box. Note that there are typically more line pairs provisioned through manual cross-connect panel 201 than are presently in use. The additional line pairs allow for growth and, in the example, for swapping out when needed. Furthermore, the number of exchange-side line pairs (i.e., 211-1 through 211-M) and subscriber-side line pairs (i.e., 212-1 through 212-N) can be different from each other (i.e., M and N can have different values).
Manual cross-connect boxes are relatively inexpensive because they are passive devices requiring no power source. They are easy to use, requiring relatively little training on the part of the technician. Furthermore, the practice of using jumper wires to connect one punchdown block to another significantly reduces confusion as different line pair combinations get rewired over time.
Disadvantageously, manual cross-connect boxes cannot be reconfigured remotely, requiring trips by the technician to each cross-connect that has to be reconfigured. Because of this inconvenience, tests and provisioning that ordinarily would be tried are possibly infeasible. Furthermore, a problem with reconfiguring manual cross-connect panel 201 is the possibility of technician error. Typically, there are dozens, if not hundreds, of line pairs at a cross-connect. Even though the wires are color-coded, it is possible that the technician swaps in the wrong wire pair or does not make a solid, durable splice. Again, consider that when swapping in a new line pair, the technician has a chance to make an error in two places: at the exchange-side of the impairment and at the subscriber-side of the impairment.
FIG. 3 depicts automated cross-connect matrix 301 of the prior art, which joins a plurality of exchange-side line pairs (i.e., 311-1 through 311-M) and a plurality of subscriber-side line pairs (i.e., 312-1 through 312-N). Sanford et. al. in U.S. Pat. No. 5,912,960 teach an apparatus and method that can be used to make an automated cross-connect. As in the case of manual cross-connect panel 201, there are typically more line pairs provisioned through automated cross-connect matrix 301 than are presently in use. The additional line pairs allow for growth and, in the example, for swapping out when needed. Furthermore, the number of exchange-side line pairs and subscriber-side line pairs can be different from each other (i.e., M and N can have different values).
Automated cross-connect matrix 301 represents an improvement over manual cross-connect 201, in that most reconfigurations can be performed without a technician having to make a trip or two to the local loop. Automated cross-connect matrix 301 is controlled from presumably a convenient location (e.g., the serving central office, etc.), so a swapping of one line pair for another can be performed conveniently in less time, probably with fewer errors and at lower labor cost.
However, automated cross-connect matrix 301 has some disadvantages. As a new cross-connect serving a new group of subscribers (e.g., new housing development, new office park, etc.), automated cross-connect matrix 301 can represent a significant initial investment cost. The cross-connect can conceivably join any exchange-side line pair with any subscriber-side line pair, requiring a relay or switch for each pair combination, making automated cross-connect matrix 301 more expensive than manual cross-connect panel 201. As a, replacement cross-connect to an existing manual cross-connect, installing automated cross-connect matrix 301 can result in significant downtime. Line pairs serving subscribers have to be disconnected from the existing cross-connect, the existing cross-connect has to be removed, the new cross-connect has to be installed, and the line pairs have to be reconnected into the new cross-connect. Finally, it is often sufficient to automate a portion of the line pairs at a cross-connect, such that installing automated cross-connect matrix 301 would be excessive for serving the actual need.
There exists a need for a practical automating of re-mapping the pair connectivity of some or all of the line pairs within a local telecommunication network. Specifically, a need exists for the convenience, speed, reduced likelihood of errors associated with automating line pairs at a cross-connect in a local loop without the expense, downtime, and lack of scalability of the automated solutions in the prior art.